Solar and wind energy provide renewable, non-polluting energy sources, as opposed to conventional non-renewable, polluting energy sources, such as coal or oil. Because of this, solar and wind energy have become increasingly important as energy sources that may be converted into electricity. For solar energy, photovoltaic panels arranged in an array typically provide the means to convert solar energy into electrical energy. Similar arrays may be implemented for harvesting energy from wind or other natural energy sources.
In operating a photovoltaic array, maximum power point tracking (MPPT) is generally used to automatically determine a voltage or current at which the array should operate to generate a maximum power output for a particular temperature and solar irradiance. Although MPPT for the entire array is relatively easy to perform when the array is operating under ideal conditions (i.e., the same irradiance, temperature and electrical features for each panel in the array), when there are mismatches or partially shaded conditions, MPPT for the array as a whole is more complicated. In this situation, MPPT techniques may not provide accurate results due to relative optima of the multi-peak power-to-voltage characteristics of the mismatched array. As a result, only a few of the panels in the array may be operating ideally. This causes a drastic drop in power production because, for an array that includes strings of panels, the least efficient panel in a string determines the current and efficiency for the entire string.
Because of this, some photovoltaic systems provide a DC-DC converter for each panel in the array. Each of these DC-DC converters performs MPPT to find a maximum power point for its corresponding panel. However, a DC-DC converter in this system may be deceived into selecting a local maximum for operating its panel instead of the panel's actual maximum power point. In addition, the use of multiple DC-DC converters in such a system results in electrical losses incurred in operating the converters, which reduces the efficiency of the entire system.